This invention relates to an apparatus for dispensing liquid from a container using a liquid pumping means having an actuator defining a liquid dispensing channel through which liquid is dispensed. In particular, but not exclusively, the invention relates to an apparatus for dispensing water-borne liquid products.
Satisfactory operation of such apparatus relies upon the dispensing channel remaining unclogged by deposits which may accumulate due to congealed residues of the product between successive actuations.
It has been proposed in co-pending application U.S. Ser. No. 07/805,659 to purge the dispensing channel by releasing compressed air through the dispensing channel during a terminal portion of the dispensing stroke when actuating the liquid pumping means thereby purging any residue which might otherwise lead to clogging. A disadvantage of such compressed air purging is that the terminal portion of the dispensing stroke will dispense the residue as an aerosol spray but with progressively different characteristics to the normal spray and sputtering of relatively large droplets will be ultimately produced.
A further disadvantage is that in this arrangement the dispensing channel is purged satisfactorily only if the dispensing stroke is fully completed. If the travel of the actuator is insufficient to complete the normal dispensing stroke then the purging action will be curtailed or may even be completely omitted from the cycle of operation.
It is an object of the present invention to purge residues from the dispensing channel without degrading the spray characteristic of the apparatus during the dispensing stroke.
A further object of the present invention is to return the residues to the container.
A further object is to admit air to the container following actuation of the pumping means in order to avoid progresive build up of vaccuum in the container.
A further object of the present invention is to provide a liquid pumping means in which the relatively slidable parts maintain continuous sealing contact to thereby avoid clogging.